A fluorescent lamp is a gas-discharge lamp that uses electricity to excite mercury vapor or other rare earth gases included in a fluorescent tube. The excited atoms produce shortwave ultraviolet light or shortwave radiation that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful light more efficiently than an incandescent lamp. Lower energy cost typically offsets the higher initial cost of the lamp. Fluorescent lamp fixtures are more costly, in part, because they must include a ballast used to power the fluorescent lamp so as to regulate the flow of current through the anode and cathode of the fluorescent lamp.
While large fluorescent lamps have been mostly used in commercial or institutional buildings, Compact Fluorescent Lamps (CFLs), or Compact Fluorescent Tubes (CFTs), are now also available in the same popular sizes as incandescent lamps and are used as an energy-saving alternative in homes. Compared to general service incandescent lamps or High-Intensity Discharge (HID) lamps, CFLs use less power for a similar light intensity and have a longer rated life. Like all fluorescent lamps, CFLs contain mercury, or non ROHS (Removal Of Hazardous Substances) compliant materials which complicates their disposal. CFLs also radiate a different light spectrum from that of incandescent lamps. Improved phosphor formulations have improved the subjective color of the light emitted by CFLs such that some sources rate the best “soft white” CFLs as subjectively similar in color to standard incandescent lamps or HID lamps.
Recently, the application of Light Emitting Diodes (LEDs) in residential, commercial, industrial and institutional illumination has become more and more popular. Compared to common fluorescent or HID lamps, for example, LEDs are more durable in nature, consume less power, have longer lamp life, emit generous amounts of light, produce less heat, offer a wider range of light colors and are environmentally friendly.
One drawback, however, is that existing LEDs are not capable of operating with variable inputs such as varying frequency, current, voltage and magnetic fields. For example, the ballasts used in fluorescent lamp fixtures to power fluorescent lamps have variable outputs. The output of fluorescent lamp ballasts varies widely in voltage, frequency, and current, dependant on the make and model. LEDs operate at a precise voltage and precise current flow. Any electrical energy source will require conditioning to establish the correct DC voltage for the LED array. A power supply which can receive a wide range of voltage, frequency and electrical waveforms and convert this to a precise output voltage, is required to operate LEDs correctly.
In order to provide a LED-based replacement to traditional fluorescent lamps in common fluorescent lamp fixtures, the limited operation of existing LEDs with respect to their power supplies requires that existing fluorescent lamp fixtures be retrofitted. Retrofitting a fluorescent lamp fixture with existing LEDs entails the removal of the existing ballast and rewiring of the fixture with either an external electrical supply or a direct (AC or DC) voltage to the LEDs, via a power supply. Retrofitting a fluorescent lamp fixture requires in most cases the services of an electrician to meet or adhere to local, provincial, state, and/or federal building codes. A direct bulb replacement, i.e.
without the need of a retrofit, of common fluorescent lamps is therefore not possible with existing LED technology.